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How do I have actions occur when a field gets changed in one of my models? In this particular case, I have this model:
class Game(models.Model): STATE_CHOICES = ( ('S', 'Setup'), ('A', 'Active'), ('P', 'Paused'), ('F', 'Finished') ) name = models.CharField(max_length=100) owner = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) started = models.DateTimeField(null=True) state = models.CharField(max_length=1, choices=STATE_CHOICES, default='S') and I would like to have Units created, and the 'started' field populated with the current datetime (among other things), when the state goes from Setup to Active.
I suspect that a model instance method is needed, but the docs don't seem to have much to say about using them in this manner.
Update: I've added the following to my Game class:
def __init__(self, *args, **kwargs): super(Game, self).__init__(*args, **kwargs) self.old_state = self.state def save(self, force_insert=False, force_update=False): if self.old_state == 'S' and self.state == 'A': self.started = datetime.datetime.now() super(Game, self).save(force_insert, force_update) self.old_state = self.state 
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Use update_fields in save() If you would like to explicitly mention only those columns that you want to be updated, you can do so using the update_fields parameter while calling the save() method. You can also choose to update multiple columns by passing more field names in the update_fields list.
Django Triggers is a light-weight framework for having one part of an application generate a trigger while another part responds to to it. Triggers are persistent and can be scheduled to be processed at a later time.
This field can be useful as a primary key of an object if that object extends another object in some way. For example – a model Car has one-to-one relationship with a model Vehicle, i.e. a car is a vehicle. One-to-one relations are defined using OneToOneField field of django.
It has been answered, but here's an example of using signals, post_init and post_save.
from django.db.models.signals import post_save, post_init class MyModel(models.Model): state = models.IntegerField() previous_state = None @staticmethod def post_save(sender, instance, created, **kwargs): if instance.previous_state != instance.state or created: do_something_with_state_change() @staticmethod def remember_state(sender, instance, **kwargs): instance.previous_state = instance.state post_save.connect(MyModel.post_save, sender=MyModel) post_init.connect(MyModel.remember_state, sender=MyModel) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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